ARMS assay to detect the JAK2 2343G > T in genomic DNA. (A) Representative results. Tracks 5 and 6 show a normal genotype; tracks 1 and 3 show a mutant band that is weaker or similar intensity to the normal band and were therefore scored as heterozygous for the 2343G > T mutation; tracks 2, 4, 7, and 8 show a mutant band that is stronger than the normal band and were therefore scored as homozygous for the mutation. Tracks 9 and 10 are negative controls and M is the 1-kilobase (kb)+ DNA ladder (Invitrogen, Paisley, United Kingdom). (B) Sensitivity of the ARMS assay. DNA from a homozygous patient with minimal residual wild-type allele was diluted with normal DNA and amplified. The ARMS assay is routinely capable of detecting V617F at a dilution of 1% to 2%. (C) Schematic outline of the assay. Primers FO and RO flank JAK2 exon 12 and should generate a control 463-bp band in all cases. Primers Fwt and RO generate a 229-bp wild-type (2343G)-specific product and primers FO and Rmt generate a 279-bp mutant (2343T)-specific product.